The recently remarkable advance in robotization technology in many industrial machines extensively requires any guide unit that is high in sliding performance as well as operational speed. To cope with the requirements stated earlier, the roller chain has been developed in which more than one rolling element of cylindrical roller is held in the retainer to keep any adjacent rolling elements from coming into direct engagement with one another, and also there have been practically developed the linear motion guide units having therein the roller chain constructed as stated earlier.
A roller chain of the type as recited earlier is known as disclosed in, for example Japanese Patent Laid-Open No. 1998-110728. The prior roller chain is comprised of more than one cylindrical roller adapted to roll through a recirculation circuit in close succession, a separator adapted to space any two adjacent rollers away from one another, and a flexible belt adapted to connect the successive separators to each other. Any two adjacent separators come into sliding contact with the circular outside surface of the roller rolling between the leading and trailing separators, thereby keeping the successive rollers in spaced parallel relation to make certain of the smooth rolling of the roller throughout the recirculation circuit. With the prior roller chain constructed as stated earlier, the separators come into the circular outside surface of the associated roller across an axial overall length of the roller to keep the roller against moving on the skews, especially serving to keep the roller in the direction normal to the traveling direction in the recirculation circuit.
Another example of the conventional chain of rolling elements is disclosed in, for example Japanese Patent Laid-Open No. 2001-165169 in which a plurality of rolling elements is received in recesses formed in an elongated carrier belt for free rotation, one to each recess. The carrier belt is made up of spar elements extending in the longitudinal direction and a plurality of rung bars extending in the transverse direction, which are combined together in the form of a ladder to define successive recesses where the rollers are accommodated for free rotation, one to each recess. The rung bars are made concaved midway between their lateral edge regions, just which come into sliding contact with the associated roller.
Meanwhile, the prior linear motion guide unit using rolling elements of cylindrical roller enables to carry larger load compared with the linear motion guide unit of another type having balls, but vulnerable to an adverse happening where the rolling axis of the roller would be tilted when the load varies, that is to say, the roller might be likely to experience any skew movement. Moreover, the conventional linear motion guide units of the sort as stated earlier, as undergoing a large thrust load in the axial direction thereof after the roller has moves on the skew, is much tough in posture control of the roller.
Compared with the linear motion guide unit of the sort having the balls, the linear motion guide unit using the cylindrical rollers is less in space to reserve lubricant therein for lubrication of the rollers rolling through the recirculation circuit. In addition, the roller, unlike the ball, is apt to have any danger of the stripping of lubricant from the rolling surface of the roller. Thus, the linear motion guide unit using the cylindrical rollers needs more frequent replenishment of lubricant.
With the roller chain constructed as recited earlier, any interval between any leading and trailing rollers is made up for the associated separator and, therefore, it is tough to make certain of the provision of space enough to reserve lubricant therein. With the linear motion guide unit of the sort constructed to use the roller chain, moreover, inside guide walls making sliding contact with axially opposite circular ends of the roller are made of other members, which are prepared separately from the slider carriage. This construction is unsuitable for carrying large thrust loads against the axially opposite circular ends of the roller. Instead, an alternative construction is developed in which the roller is sandwiched between any leading and trailing separators to be prevented from moving on the skew.
The roller chain constructed as stated just earlier is needed to make a clearance between the roller and any one of the leading and trailing separators as small as possible to keep the roller against movement on the skew while allowing the roller to make free rotation. To cope with this, the roller chain had to make it by any specific production process including, for example integral molding. With the roller chain constructed as stated just earlier, the spar elements of the carrier belt experience repeatedly partial flexure midway any two adjacent separators jointed to the spar elements because the separators are made resistant against flexure. Thus, the prior carrier belts are easy to suffer bending fatigue.
With the roller chain made as stated earlier in the form of the ladder in which a pair of lengthwise spar elements is connected together with successive separators or lung elements that are spaced away from one another at a fixed interval, the separators are each made of a rectangular plate that is jointed to the spar elements at only middle areas in height on the lateral edge regions thereof. As a result, the separators of rectangular plates jointed to the spar elements at only middle areas in height on the lateral edge regions thereof, since easily coming into engagement at their contours with any other member, may suffer any unwilling accidental loads, so that they are tough to continue keeping their proper posture with steady. Moreover, the separators, as made concaved midway between their lateral edge regions, are rendered less in thickness and eventually blamed for the reduction in mechanical strength of the roller chain. Besides, as the separators are made resistant against flexure, the spar elements experience repeatedly partial flexure and thus are easy to suffer bending fatigue.